1. Field of the Invention
The present invention relates to a method of manufacturing Distributed FeedBack (hereinafter abbreviated as xe2x80x9cDFBxe2x80x9d) type semiconductor laser devices and to a DFB type semiconductor laser device.
2. Related Art
DFB type semiconductor laser devices are well-known as devices for use with light communications systems such as light CATV, shortwave lasers making use of SHG (Second Harmonic Generation) devices, pump light sources for small-sized solid-state lasers, light measurement arts or the like.
FIG. 1 shows a conventional DFB type semiconductor laser element. Laminated on a substrate 1 composed of n+-InP are a lower clad layer 2 composed of n-InP, a lower guide layer 3, an activated layer 4, and an upper guide layer 5, which are composed of InGaAsP having different compositions. Further above the upper guide layer 5 is an upper clad layer 6 composed of p-InP partly having a ridge. Provided on flat portions on both sides of the upper clad layer 6 is a grating layer 6a and provided on top of the ridge is a contact layer 7 composed of InGaAsP. Arranged on the grating layer 6a is an inorganic protective layer 8 composed of a silicon compound such as water glass. Also, electrodes 20, 21 are formed on the contact layer 7 and on an underside of the substrate 1.
With conventional DFB type semiconductor laser devices, a ridge is formed to confine a generated light in a three dimensional space. However, a process of forming such a ridge, and a process of forming a window, which is required for an electrode to be provided on the top of the ridge, with high accuracy while aligning it, are extremely complicated and responsible for an increased cost.
The present invention has been developed in view of the above-described problem, and is aimed at providing a DFB type semiconductor laser device, which can be readily manufactured without any complicated process, and also provides a method of manufacturing the same.
A DFB type semiconductor laser device according to the present invention comprises a laser substrate, a grating layer, an insulating layer and an electrode layer, which are laminated in this order, the insulating layer including a through groove or grooves extending to the grating layer in a direction, along which a resonator of the laser device is formed, and the electrode layer contacting the grating layer and the clad layer.
Also, a method of manufacturing a DFB type semiconductor laser device, according to the present invention, comprises the steps of forming a laser substrate including at least a waveguide layer and a clad layer, forming a grating layer on the top surface of the laser substrate; forming an insulating layer having a through groove or grooves extending to the grating layer in a direction, along which a resonator of the laser device is formed, forming an electrode layer made of a high refractive material on the insulating layer, and forming a further electrode layer on the bottom surface of the laser substrate.